Many of the devices, tools and machines that are in common use today, rely extensively on integrated circuits, semiconductors and other small components. Whereas the benefits from these types of devices are obvious, there are some difficulties that accompany their use. One such difficulty is that of maintaining the cleanliness of the devices themselves. Due to their small incredibly minute size and the fragile nature of their construction, specialized cleaning methods have been developed.
One method for cleaning integrated-circuit silicon wafers, hard disk platters and small mechanical components is to use spin clean systems. These spin clean systems involve the use of a high pressure water jet, at approximately 1200 psi. The water jet is vertically directed upon a rotating part to be cleaned, with the part being positioned therein below. The nozzle of the jet is attached to a reciprocating arm, so that the entire part can be accessed and cleaned. Often, though, the high pressure of the water impinging on the part causes damage. Also, high pressure spin clean systems are not economically well suited for a high volume manufacturing environment. These systems are relatively expensive, and require large quantities of ultra-pure, deionized water and the use of high pressure filters, which are needed to maintain the high water pressure and the purity of the water.
Another method of cleaning integrated circuit silicon wafers and hard disk platters is to immerse them in a cleaning tank filled with a cleaning solution. A periodic control signal is then applied to an ultrasonic vibrator, which typically consists of a piezoelectric element. The periodic control signal has a frequency equal to the natural frequency of the piezoelectric element. This allows the element to vibrate at its natural frequency, thereby radiating an ultrasonic energy into the cleaning solution. The radiated ultrasonic energy produces a cavitation in the cleaning solution, which generates shock waves to clean the parts immersed in the cleaning solution. To maintain uniform cleaning, it is necessary to generate the cavitation uniformly in the cleaning solution, without becoming dispersed throughout the solution. This is accomplished by radiating the ultrasonic energy at a higher frequency. The higher the frequency, the less likely any damage will be caused to the part. Conversely, if a stronger cleaning capability is desired, the ultrasonic energy is applied at a lower frequency.
The ultrasonic vibrators, are also available with multiple piezoelectric elements, having respective different natural frequencies. However, these vibrators are difficult and expensive to manufacture. Another problem is that the cavitation distribution becomes unstable due to the natural frequencies of the piezoelectric elements tendency to vary as a result of both the piezoelectric element manufacture, and the heat produced when the ultrasonic vibrator is oscillated. Consequently, it is difficult to clean many parts uniformly by using cavitations processes.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention, however the following U.S. patents are considered related:
______________________________________ U.S. PAT. NO. INVENTOR ISSUED ______________________________________ 5,462,604 Shibano, et al 11 October 1995 5,432,969 Oh 18 July 1995 5,368,054 Koretsky, et al 29 November 1994 5,333,628 Ogata, et al 2 August 1994 ______________________________________
The U.S. Pat. No. 5,462,604, Shibano, et al discloses an ultrasonic vibrator that has a single natural frequency for radiating ultrasonic energy into a cleaning solution to clean and deburr workpieces that are immersed in the cleaning solution. A plurality of oscillating signals having respective different frequencies, which are integral multiples of the natural frequency of the ultrasonic vibrator are generated, and successively produced. These signals are applied for respective periods of time to generate a composite signal which is composed of a timed series of oscillating signals. The composite signal is applied as a drive signal to the ultrasonic oscillator to oscillate the ultrasonic vibrator.
The U.S. Pat. No. 5,432,969, Oh discloses a washing method and a washing apparatus capable of obtaining a washing or cleaning effect by mechanical energy obtained by cavitation phenomena or nonlinear oscillation of micro air bubbles generated during the resonance of a multi-phase medium using low frequency waves. This invention eliminates the use of any pulsator, therefore, it is possible to considerably reduce the phenomenon that clothes get twisted or tangled. Moreover, the electric power consumption in washing or cleaning is greatly reduced.
The U.S. Pat. No. 5,368,054, Koretsky, et al discloses an ultrasonic jet semiconductor wafer cleaning apparatus for removing debris from a surface of a semiconductor wafer as the wafer is rotated about a prescribed axis in a cleaning plane. The apparatus comprises a housing having a principal axis, an inlet port, and an outlet port. A means for producing focused ultrasonic waves of acoustic energy that are concentric with and incident to the outlet port form a jet stream of cleaning liquid, which is released through the outlet port. A focal point positioning means for adjustably positioning a focal point of the focused ultrasonic wave producing means is located between a first focal point position and a second focal point position along an axis. A means coupled to the housing for sweeping the housing in an reciprocating manner along a sweep path is also included.
The U.S. Pat. No. 5,333,628 Ogata, et al discloses a continuous ultrasonic cleaning apparatus having excellent cleaning efficiency and holding/carrying capability of the product-to-be-cleaned. The continuous ultrasonic cleaning apparatus utilizes a cleaning agent receiving/storage bath having a cleaning agent supplying/adding function for the cleaning bath positioned there below and an ultrasonic oscillator. Net conveyors for holding the product-to-be-cleaned are used and synchronized for carrying the product-to-be-cleaned. No stain or water marks are formed and an equivalent cleaning quality can be achieved as that when using fulone. Furthermore, by using an oxygen-free water and purging inert gas for the entire receiving/storage bath, any product having a propensity to be easily corroded can be effectively cleaned.
For background purposes and as indicative of the art to which the invention is related reference may be made to the remaining cited patents.
______________________________________ PATENT NO. INVENTOR ISSUED ______________________________________ 3,681,626 Puskas 1 August 1972 3,873,071 Tatebe 25 March 1975 4,183,011 Massa 8 January 1980 4,799,167 Sarr 17 January 1989 4,834,124 Honda 30 May 1989 4,979,994 Dussalt, et al 25 December 1990 4,991,609 Browning 12 February 1991 5,203,362 Shibata 20 April 1993 5,203,798 Watanabe, et al 20 April 1993 5,227,001 Tamaki, et al 13 July 1993 5,307,680 Drescher-Krasicka 3 May 1994 5,322,082 Shibaflo 21 June 1994 5,337,446 Smith, et al 16 August 1994 5,345,958 Otsuka 13 September 1994 5,377,709 Shibaflo 3 January 1995 5,378,287 Pedziwiatr 3 January 1995 5,409,594 Al-Jiboory, et al 25 Apri1 1995 5,412,585 Hamilton 2 May 1995 5,444,892 Ris, et al 29 August 1995 ______________________________________